Abstract: Mosaic coke is a kind of special artificial carbon material, which is usually used as the raw material to produce high-quality nuclear graphite. The quality of graphite has been usually focused on the properties of mosaic cokes. In order to investigate the influence of the quinoline insoluble (QI) content of heavy-phase pitch on the micro-structure and properties of mosaic coke, 9 kinds of heavy-phase pitches with varied QI contents were used as the raw materials to produce series of mosaic cokes in this study. Optical micro-scope, scanning electronic micro-scope, X-ray diffraction, Raman spectrum and curve-fitted methods were used to judge the micro-structure of 9 kinds of mosaic cokes. Also, the micro-strength of mosaic cokes was determined. The results show that the higher content of QI in heavy-phase pitch has the mosaic structure easier to be produced during the liquid-phase carbonization process. What’s more, with the increase of QI content, the content of regular carbon microcrystals decreases, but the content of amorphous carbon and micro-strength are improved. When the QI contents in the heavy-phase are higher than 7%, the derived mosaic cokes have the total contents of mosaic structure (the sum of fine mosaic structure, medium mosaic and coarse mosaic) higher than 82% and the micro-strength higher than 85%. In other words, the heavy-phase pitch with the content of QI higher than 7% is a promised raw material to produce high-quality mosaic coke.